1. Field of the Invention
The present invention generally relates to a power generator system and, in particular, to an improved power generator system incorporating a generator driven by a prime mover that operates at controlled speeds.
2. Description of the Related Art
Portable power supplies, such as electrical power generator systems that incorporate a generator driven by an engine, are popular for many uses. In an exemplary portable power supply disclosed in JP-A-H5-18285, the engine-driven generator produces raw AC power (e.g., the produced voltage and frequency varying with engine speed). The raw AC power is then converted to a higher quality AC power output. A controller adjusts the speed of the engine to regulate the AC power produced. For this purpose, a current sensor is used to sense the current level of the AC power output and this information is received by the controller. The controller calculates a reference engine speed based upon an output signal from the current sensor and controls the engine (e.g., controls a throttle valve of the engine ) such that the engine's speed generally matches the reference engine speed.
Typically, a noise-suppressing housing surrounds the engine, the generator and other engine/generator components. Heat produced by the engine and the generator warms the air within the housing, which can reduce the generator's performance. Relatively high temperatures within the housing can affect the operations of the engine and the generator. Particularly, the efficiency for generating power can deteriorate as the internal resistances of the components increase with increased temperature.
As the relatively high temperature within the generator housing continues to increase, the controller can erroneously determine that a load device, which is connected to output terminals of the generator, does not need as much power as before because the current sensor indicates that the output current is decreasing. The decrease of course is rather due to the drop in generator efficiency. The controller thus causes the engine to decrease its speed. The output voltage consequently decreases further until the engine-driven generator can no longer supply sufficient voltage to the load device.
In order to prevent such a voltage drop from occurring, prior power generator system use a voltage sensor in addition to the current sensor. The voltage sensor provides the controller with an output signal indicating that the current load demand placed on the generator by the load device. The controller adjusts the reference engine speed based upon the output signal from the voltage sensor in addition to the signal from the current sensor. While effectively addressing the above noted problem, inclusion of both the current and voltage sensors increases the complexity of the generator system.